JP3201088B2 - Surface acoustic wave resonator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave (SAW) resonator for forming a resonator or a multimode filter using a surface acoustic wave.

[0002]

2. Description of the Related Art As shown in FIG. 2, for example, a SAW resonator is an interdigital transducer (I-digital transducer) composed of a pair of strip-shaped electrode films on one surface of a piezoelectric substrate such as quartz.
A DT) electrode 2 and reflectors 3 and 4 each formed of a strip-shaped electrode film on both sides of the IDT electrode 2 constitute a resonator.

Further, a multi-mode filter uses a vibration mode called a transverse mode distributed perpendicularly to a propagation direction of a surface acoustic wave excited by the resonator (an arrangement direction of an interdigital transducer electrode and a reflector). It is also used as a so-called SAW filter.

[0004]

As shown in FIG. 2, in the SAW resonator, the energy density in the transverse mode is not only the fundamental mode M1, but also the secondary mode M2 and the tertiary mode M.
There are also higher-order modes such as 3, and the existence of the energy density of these higher-order modes may form an unnecessary pass band on filter characteristics. Also, when used as a single SAW resonator, its characteristics may be deteriorated.

An object of the present invention is to provide a surface acoustic wave resonator that suppresses the generation of higher-order modes among surface acoustic waves in a transverse mode.

[0006]

In order to solve the above-mentioned problems, the present invention provides a piezoelectric substrate, an inter-digital transducer electrode formed of a pair of strip-shaped electrode films on the surface of the piezoelectric substrate, and In a surface acoustic wave resonator provided with a pair of reflectors provided on both sides of an inter-digital transducer electrode and formed of a strip-shaped electrode film, the inter-digital transducer electrode and the reflector are arranged in the direction of the arrangement. And a waveguide formed of a piezoelectric thin film or an insulating film on the upper surface or the lower surface of the electrode and the reflector with a width equal to or less than the intersection width of.

[0007]

The portion where the waveguide is provided on the piezoelectric substrate is thicker than the other portions by the thickness of the waveguide. Utilizing this mass effect, the propagation of the surface acoustic wave is easily concentrated on the waveguide portion, and the energy density distribution in the transverse mode of the surface acoustic wave is increased in the fundamental mode and is decreased in the higher-order mode. Suppress the occurrence of the next mode.

[0008]

FIG. 1 is a configuration diagram of a SAW resonator showing one embodiment of the present invention. 2 is different from the configuration of FIG.
The point is that the surface acoustic wave waveguide 5 is formed on the surface acoustic wave propagation path.

In the SAW resonator having this structure, an IDT electrode 2 and reflectors 3 and 4 are formed on a piezoelectric substrate 1 by an ordinary method, and a waveguide 5 is formed as a piezoelectric thin film or an insulating film by a vapor deposition method or the like. Is done.

Conversely, after forming the waveguide 5 on the piezoelectric substrate 1 by vapor deposition or the like, the IDT electrode 2 and the reflectors 3, 4
May be formed.

The width w of the waveguide 5 in the direction perpendicular to the direction of propagation of the surface acoustic wave is equal to the width of the IDT that forms a pair of strip-shaped electrode films.
A value equal to or smaller than the intersection width W of the electrode 2 is set.

The length of the waveguide 5 in the propagation direction of the surface acoustic wave is set to a value including the IDT electrode 2 and the reflectors 3 and 4. The thickness of the waveguide 5 is, for example, 0.1 to 0.1.
It is set to 1 micrometer.

According to this embodiment, the portion of the piezoelectric substrate 1 where the waveguide 5 is provided is thicker than other portions by the thickness of the waveguide. Due to this difference in mass, the surface acoustic wave is easily concentrated and propagated at the portion of the waveguide 5, and the energy density distribution is large at the center where the waveguide 5 is formed and small at the end.

As a result, the fundamental mode is mainly distributed among the transverse modes, and the distribution of higher-order modes is suppressed. In other words, the generation of higher-order modes in the transverse mode is suppressed, and almost all of the fundamental modes can be generated, so that the adverse effects of the higher-order modes on the characteristics of the resonator and the filter can be reduced.

In the above embodiments, the case where the waveguides 5 have the same thickness has been described. However, the waveguide 5 has a structure in which the center portion is thicker in the width direction than the both sides, so that the higher order mode can be obtained. The suppression effect can be increased.

[0016]

As described above, according to the present invention, in addition to providing the IDT electrode and the pair of reflectors on the piezoelectric substrate surface, the IDT electrode and the pair of reflectors are arranged in the direction in which the electrodes and the reflectors are arranged and the width is equal to or smaller than the intersection width of the electrodes. Since the waveguide is made of a piezoelectric thin film or an insulating film on the upper or lower surface of the electrode and the reflector, propagation of the surface acoustic wave is easily concentrated on the waveguide portion, and the energy of the surface acoustic wave in the transverse mode is increased. The density distribution increases in the fundamental mode and decreases in the higher-order mode, so that the occurrence of the higher-order mode can be suppressed, which has the effect of reducing the adverse effect on the resonator and the filter characteristics.

[Brief description of the drawings]

FIG. 1 is a plan view of a surface acoustic wave resonator according to an embodiment of the present invention.

FIG. 2 is a diagram showing a conventional structure and its transverse mode energy density distribution.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 piezoelectric substrate 2 IDT electrode 3 4 reflector 5 waveguide

Claims (1)

(57) [Claims] 1. A piezoelectric substrate, an inter-digital transducer electrode composed of a pair of strip-shaped electrode films on the surface of the piezoelectric substrate, and strip-shaped electrode films provided on both sides of the inter-digital transducer electrode. In a surface acoustic wave resonator having a pair of reflectors, the upper and lower surfaces of the interdigital transducer electrode and the reflector are arranged in the direction in which the interdigital transducer electrode and the reflector are arranged and have a width equal to or less than the intersection width of the electrodes. A surface acoustic wave resonator comprising a waveguide formed of a piezoelectric thin film or an insulating film.